This invention relates to a process for recovering a carboxylic acid from an aqueous media such as a fermentation broth. The carboxylic acid is made by the biological oxidation of a substrate by a microorganism.
Standard methods for recovering carboxylic acids in general, and polycarboxylic acids in particular, from fermentation broths are typically based on the physical separation of the spent microorganism cells from the aqueous phase, such as by centrifugation, followed by precipitation of the carboxylic acid as a result of pH reduction of the aqueous phase. This method is unsatisfactory for a number of reasons, the most notable of which includes the problem of physically separating the spent cells and then acidifying the cell-free broth to effect the precipitation of the carboxylic acid. The precipitation of the carboxylic acid is time consuming and the separation and isolation of the precipitated carboxylic acid is not always clean, i.e., there can be impurities which adversely affect the quality and purity of the final product.
Accordingly, there is a continuing need for improved processes for recovering carboxylic acids from a fermentation broth.
The present invention involves an improved process for the recovery of a carboxylic acid made by the biological oxidation of a substrate by a microorganism such as a yeast. Carboxylic acids are recovered from a fermentation broth by extracting the broth with a solvent containing one or more olefins without the need for first removing the spent microorganism cells. In one aspect, a cosolvent is combined with one or more olefins to create a solvent which favorably adjusts the partition coefficient. A preferred solvent for the extraction of carboxylic acids from a fermentation broth contains a mixture of tertiary-butyl acetate and diisobutylene.
In another aspect, a method for isolating at least one carboxylic acid from an aqueous mixture is provided which includes providing an aqueous mixture containing at least one carboxylic acid, contacting a solvent containing at least one olefin with the aqueous mixture, allowing the at least one carboxylic acid to separate into a solvent, isolating the solvent containing the at least one carboxylic acid from the aqueous mixture, separating the solvent from the at least one carboxylic acid, and hydrogenating the at least one carboxylic acid to produce a saturated carboxylic acid. A co-solvent may be combined with the at least one olefin.
Solvents are provided which, in one embodiment, include a mixture of a minority amount of tertiary butyl acetate and a majority amount of diisobutylene. During the process of recovering the carboxylic acids, one or more co-solvents may be included which generally aid in the process, e.g., by reducing the amount of solvent needed to remove the carboxylic acids, and/or the number of extraction cycles necessary to adequately remove the carboxylic acids from the fermentation broth.
After employing a fermentation procedure to produce a carboxylic acid, the viscosity of the fermentation broth may optionally be adjusted, preferably by heating the fermentation broth, to form a flowable liquid. The pH of a fermentation broth which contains one or more carboxylic acids may be optionally adjusted to a value of from at least about 2.0 to about 7.0. The carboxylic acid-containing broth is contacted with a solvent containing one or more olefins to extract the carboxylic acid. The carboxylic acid may then be isolated by separating crystals of the carboxylic acid from the extraction solvent. Means for isolating the carboxylic acid from the extraction solvent are known to those skilled in the art and include, but are not limited to, evaporation, distillation, melt crystallization, and crystallization. The resulting carboxylic acid may then be further purified by distillation and/or processed by hydrogenation to saturate any unsaturated carboxylic acids.